1. Field of the Invention
This invention relates to improvements in a cantilever type rolling mill employing a roll assembly adapted to transmit torque to a ring roll by frictional force produced by application of a compressive force on the opposite lateral sides of the ring roll.
2. Description of the Prior Art
For mounting a ring roll on a roll shaft of a cantilever type rolling mill for wire rods or steel rods, it has been the conventional practice to provide a tapered surface on the circumference of a roll shaft and to insert an internally tapered sleeve between the roll shaft and an axial cylindrical hole of a ring roll for the purpose of mounting the ring roll fixedly on the roll shaft and transmitting torque to the ring roll by the frictional force of its cylindrical inner peripheral surface.
With such a construction, a large tensile stress occurs at outer peripheral portions of the ring roll due to insertion of the tapered sleeve, so that a crack is very likely to take place in a direction perpendicular to the circle of the ring upon an increase of in the torque to be transmitted In a case where the ring roll consists of an ultra hard roll which is smaller in thermal expansion (about 1/2) as compared with the roll shaft and sleeve of steel, a greater thermal expansion takes place on the part of the roll shaft upon a temperature elevation, inviting cracking of the ring roll by application thereto of an excessive tensile stress. In addition, as torque transmission to the ring roll is effected solely by the frictional force of its inner surface, sooner or later most of costly ultra hard rolls have to be scrapped due to a limit in critical stress, resulting in a material increase in cost. Moreover, precision is required with regard to the pressing force of a tapered sleeve to be inserted for torque transmission by internal pressure in consideration of the above-mentioned problem of tensile stress of the ring roll.